Refactor stage1's and stage2's main.c files

Fix bug in crt0

Make di.c accept arbitrary FB addresses, fix flickering issues

Fix faulty IRAM check in check_32bit_address_range_in_program

Fix inverted condition issue in check_32bit_address_range_loadable

[stage1] Fix DEFAULT_BCT0_FOR_DEBUG

Rewrote crt0, init, and chainloading code ...

start.s, init.c, linker.ld and linker.specs are meant
to be re-used by user applications, should they remove the defines
from init.c and the .chainloader* sections from the linker script

fusee: fix boot partition selection

fusee: fix regression in card detection

Upgrade FatFs to R0.13b

Don't pass the mmc struct around

Fix const-correctness issue in sdmmc.h

Normalize drivers between stage1 and 2

[stage1] support utf8 in fatfs

Instead of passing FatFS structs around, unmount; other changes

fusee: fix an obvious sdmmc error (oops)

fusee: sdmmc: clean up and prepare for better SD/MMC/version separations

fusee: add support for SDMMC write operations

Fusee: fix typo

Fusee: Add #define requirement for pragmatic reasons.

fusee: enable sdmmc loglevel control

fusee: fix multiple-block SDMMC transfers

Move fatfs around

Change defaut BCT0 for debug

Merge SD stuff into fusee-secondary. Switch diskio to single-sector reads temporarily

Push minimally working FATFS.

fusee: make SDMMC debug printing more manageable

fusee: get uSD working, fix bad no_iopower, and abstract card differences

fusee: fix SD pinmuxing / signal integrity issues

fusee: fix drive strength and avoid a pad wear-condition